Sound-reproducing apparatus



May 15, 1928.

C. M. BOUDETTE SOUND REPRODUCING APPARATUS Filed Aug. 4, 1923 Patented May 15, 1928 CLAYTON m. I BQUDETTE. or REVERE, MASSACHUSETTS.

: sommmnraonucnm aP aa rUsi Application filed August 4,

This I invention 1 relates to: sound reproducmg apparatus and: 1s especially .-.concerned1 with the problems; presented ini the volume:

- reproductionaof: sounds transmittedby radio:

telephony; I

jIII: radio. Work; it is: now/ c'ommon pracst-i'cet'to use: so-ca-lled loud speakers? inane producing music; speechesvv andhtheilike. While these pieces-of appara'tus givevvery satisfactory: reproductions Jund'er: some" con- 1 ditions, they produce Avery; distorted results at other timesand} they give only very f-a-int andil scarcely audible reproductions under manyrcircumstances;

1 I' tzis' the chief objects of the present inven tion to devise: a loud. speaking apparatus which: Willi reproduce music, speech, orrother' sounds: truthfully preserving: the original quality'a'nd? tone. i I

' In. devices of this ch'araclter" a receiving diaphragm is caused to vibrate in accord ance Wlt-l'lrOIiIESPOIld tovthe pulsations :or

movements "of a r-transmission adevice con nected thereto," and a the present invent-ion relates .to "an novels connection; between the diaphragm and: said device for vibrating it;

that? substantially eliminates rthezidistorti-ons-v tions in: the-vibrations 0f?the receiving diaphragm; as disolos'ed in' my lietters Patent '5 or the United States No. 155 E554Hated- 9st; 20, 1925 1601 sound reproducing apparatusg sion. r

Wh ile the invention' is illustrated and -deseribedin -connectionwith loud speakfi-ng- 'ap'- paratus designed for use in radio telephony;

it can also be used. to advantage; in. other I soundreproducing apparatus,-- WhGthIf oper t;

ated "eleotro-mechanically or mechani'call jn 192s, Serial 1%:- csaws.

tureswill be particularly pointedaout' in-the Y appended claim. i

In the" accompanyingdrawings,- 'shoW-i ng' the I preferredfond of the invention,- 1

Flgure 1 is a view-partly in side ele'va tionrand partly in vertical, cross section; showing; a-diaphragm c'o'nnecte'd,-- i-Ii the novel manner hereinafterf describedytotheeleotro-magnetio' dia hgram vibrating apparatus f described in' my co pendin'gapplica tion herei nbefore referred toy-and Fig1'2'1sa view, in p'lan, of the?same* dimphra'gm and' diaphragni' vibrating appara tus'as-sho'wn in Fig. '1 -,-;With"the-horn holdmg p ate removed? f 1 Only a brief description willbe given of the illustrated diaphragm vibrating appa' ratus'sin'ce a full" disclosure of its construe? ,5575554} to which referenceent Patent No. 1 may be had;

The coiisti-uctiomillustrated comprises founpermanent magnets l, 2, 3], I -oft the horse-shoe type arranged with their-' poles ad] acent'i; magnets 1; and 1 3 being {superposed on" l gnets 2- and; 4.; The magnets-are properly spa ojed k jyzsuitahly arranged lugs 6 011* a non ma gnet'i'c supporting frame-*5 and" the Wholeisolamped toa non magneticbase plate 9 by screws-7 7 h'aving -.co'11ars 8+8 th'a't beariofi-{the'f-upper edges tithemagnets, l 1 and' 3u v l Mount-ed between th'e'poIes of the-perms nan-1; magnets is an 1 armature m; ,compr i'sin' i preferablya thin plate-pf silicon steel; "p v:-T oted -at 1 itsen'd's '1'3 'in metal yoke pieces- 1414 seoured to the frame -*5 ","-"and' provided at one corirerywith' a" lug 15 which roj eats beyond the lateral faces -;'of the magnets and' 'rfThis ll'i-ggfil'ii is-lconnectedfby means of a" rod or other uitable;transmissi n d'w Vice: "1& with th e*-central-portion" of a re silie'nt 1 diaphragm 17." The marginal er: tion' of tlfis diaphragm is clamped With-even marginal pressure, as" usual} between two? rubber: rings 18"'-"18 located in" an annularrecess fermedfirr'the lower "part-"of the base" plate 9; the' rings being held inthi's" recess byi a -plate 19 secured to the base-*9 byrewse 20+201**The "diaphragm:preferably-is made" 'lh'enature o-f the invention-Will be readi-f of imica, andthe-supporting"means just as I 1y understood from: tlfe foll 'owing" deserip tion when read in" connectionwithfi the accompanying drawings; and the novel fe'a- J scribedf leaves the 5 circular central l-area of this" di aphragmffree to" vibrate; as usual in apparatus of this type. The plate 19 is ro:

' vide d with a hollow nipple 23 located opposite the central portion of the diaphragm 17, to which nipplea horn or equivalent device may be connected. i

'While the armature 12 may oscillate about its pivotal connectionto the yoke pieces let-14, its connection to the resilient diaphragm 17 holds it normally in a neutral or central, position. The armature l2 vis oscillated about its axis by means of a coil 25 which encircles it, with the plane of the windings lying at right angles to the axis oi the armature. The effect upon the armature.

rent flowing through the coil, but very feeble currents will produce relative powerful oscillations of the armature.

I These oscillations will be positively trans mitted to "the diaphragm 17 through the transmission rod 16, thus producing in the diaphragm vibrations varying with the fluctuations of the current in the coil 25.

In using an evenlyclamped circular diaphragm to reproduce the sound waves, as is rhe practice in most sound reproducing 1nstruments, thereis a tendency to accentuate or emphasize those sounds vhaving a. irequencywhich agrees with'the naturalirequency period of the diaphragm. Th s is very largely responsible for. the distortion produced inthe present loudspeakers.

II have. discovered a means for substantially, eliminating the distortions produced in prior sound reproducing instruments due to the naturalfrequency period of the diaph ragm ln thesej prior instruments thev connection from the transmission mechanism to the-diaphragm is generallv made at the geometrical center of the diaphragm. I

i have found that by decenter-ing this connecperiodof thediaphragm appears to bejsubtion without stiffening a considerable area of the diaphragm the natural frequency stantially destroyedand that a very marked increase in -cle'arness of tone and :taithltulnessiof reproduction is effected. This sen sitiveness to tonal values is obtained because the decentering of the. vibrating arm connection prevents the diaphragm from rei would otherwise respond. This decentering producing or accentuating frequencies of a particular periodto which the diaphragm need not be great; for instance, in a two inch diaphragm a decentering of one-six-. teenthrof an inch produces very satisfactory results. '1 a J The preferred construction is illustrated by the drawings, both figures showing the transmission rod .16 connected totlie diaphra'gm" Nod-center, that is, the connection is not exactly to the geometrical center of the area of the diaphragm within the pe ripheral clamping rings 18. v

To indicate this clearly, the geometrical center of the diaphragm area having a naturalfrequency period is indicated on Fig. l by the arrow 22, and on Fig. 2 by the center-cross 22. It Will be observed that this ointdoes. not coincidewith the point of connection of the of it,jthat is, the rod connection is de-cen= tered. The diaphragm end of the rod 16 is connected directly to the diaphragm by being entered in a hole, made for its'recep-Y tion atthe desired [off-center point, and then clamped to the diaphragm inany usual or convenient manner that provides :t'or normal projection of the clamped end from the diaphragm. In the: present instance a.

normal projection of the, rod 16 is obtained bv providing it with a shoulder-nearv its r0d416but'that the latter point is at onesideend, the face of which is in aplane normal to the'axis ofthe rod." The rod end beyond this shoulder, that projects-through a :hOle

in the diaphragm, receives a threaded nut; by which the diaphragm is clampedagainst said shoulder, all as. clearly shown-at 24in toiadvantage not only in receivers of reproduc'ers which are operated electro-lmagneti-j cally, but also in .those which are operated This feature of the invention can be used Inn mechanically.- While the transmission lOda: 16 is illustrated asastraightibar connecting v the art willrunderstand' that it is within the scope-of the invention to use. a bent rod the diaphragm and armature, those skilled in v when the construction ofv'the apparatus in;

which the diaphragm isto beused is'suchas to require-it; NVhen either arbent or a straight transmission rod16 is used, the fspote connection .tOrthQ diaphragm formed by the rod'clamp 24c-is such that the portion of the vibration; area stiffened by. the rod clamp, is sosmall as to cause no restriction to the natural responsive movement of the dia phragm. The relative sizefofthe spot-con-f nection, in the illustrated form, may be visu-, alized by comparing the area of the diaphragm 17 with that of-the rod clamp24, in Fig. 2. It will beobserved'that the T111157,

trated transmission connection leaves the diaphragm wholly unrestrained exceptfor its marginal clamp, that is, the free or nat uv ral response of the diaphragm to all f re-- quencies, i. e; to all impulses given toj the transmission rod, is not restrictedby increa sing the stiffness coefficient. This is, highly important in reproducing or regenerating signals bymeans of the weak current-from a radio broadcast'receiver. Pertection in reproduction is possible only when the reproducing instrument is so sensitive as to enable it to respond accurately to all impulses, regardless of the frequency, generated at the armature end of the transmission rod. This means an elimination, so far as mechanically possible, of all the reactive forces that,

' ofiPcenter, spot-connection of the transmis- SlOIl rod produces an infinite number of lines or vibration loops of equal sensitivity, each one differing in length from all the others.

Consequently the diaphragm has no specific 1 or natural frequency period and, because it will not unduly respond to ,or accentuate some particular frequency but yet does respond freely to extremely weak impulses, distortion of sound'caused by these defects in prior instruments is eliminated.

From the foregoing it will be understood why the configuration of the transmission rod connection-must be in the form of a small spot, rather than in the form of an elongated slit or slot, which would cause the st-iifening of such a large circular area as to prevent the diaphragm from responding in the manner just described.

I have found in actual practice that this apparatus reproduces music, speech, and the like, transmitted by radio, clearly and faithfully and is far superior to prior forms of apparatus of this character of which I have been able to learn. Thediiference is particularly marked where a volume reproduction of the transmitted sounds is made.

It will be clear tothose skilled in the art to which this class of apparatus pertains, and i with the general objects of the present invention in view, that changes may be made in the details of structure, the described and illustrated embodiment thereof being ine tended as an exploitation of its underlying essentials, the features whereof are definitely stated in their true scope in the'claim herewith. 7

Having thus described my invention, what I desire to claim as newis:

In a sound reproducing apparatus, the

combination of a circular diaphragm formed of material of a uniform thickness throughout having a hole therethrough located to one side of its geometrical center, a transmission rod mounted at one side of the diaphragm having one end projecting through said hole, means for securing the rod in said hole by clamping pressure that stiifens only an extremely small spot on the surface of the diaphragm, and meansfor clamping the diaphragm at its periphery in a manner to provide a circular vibration area the center of which is at said geometrical center.

CLAYTON M. BOUDETTE. 

